Engineered metal crib for use as a support structure

ABSTRACT

This invention provides improvements through an engineered metal crib element for construction of cribs in mines to provide support between two surfaces and use of crib elements to construct cribs. The engineered metal crib element consists of a center elongate structural element and at least two outer load carrying steel members. The outer load carrying members may be composed of solid or hollow metal with one or more reinforcements within each load carrying member. Each outer load carrying member is attached to the center elongate element at the distal ends of the elongate structural element. The crib structure may be constructed by superimposing only these steel crib elements in 2×2 layers, 2×3 layers, 3×3 layers or in any other suitable layering system. The engineered metal crib elements are lightweight, have controllable higher stiffness and load carrying capacity than current wooden cribs, have engineered plastic yielding characteristics and allow much lower resistance to air flow in underground mine roadways.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and benefit of an earlier filed co-pending Provisional Patent application Ser. No. 61/323,537 filed Apr. 13, 2010 entitled Engineered Steel Crib for Use as Mine and Tunnel Support.

FIELD OF INVENTION

This invention relates primarily to the mining, tunneling, and construction industries and, more specifically, to an engineered steel crib for the support of hanging wall and foot wall, roof and floor, or upper and lower surfaces in underground mining, or providing temporary support for heavy structures such as ships, cars, houses or buildings being relocated or receiving foundation work.

BACKGROUND OF INVENTION

Wooden posts and wooden cribs, or chocks, are probably the oldest support systems used in the mining and construction industries. A wooden post, typically 4 inches to 10 inches in diameter or square cross-section, loaded axially provides support between two points. A wooden crib or chock provides support over a larger area, typically varying from a 30 to 72 inches square or rectangle. Wooden posts and wooden cribs are extensively used in the mining industry even today.

A wood crib consists of layers of two or more parallel timbers with adjoining layers placed at right angles to each other. Thus, the number of parallel timbers in each direction determines the number of contact areas through which load is transferred or resisted. For example, a 2-by-2 crib means two layers of timber in each direction, resulting in 4 contact areas. A 2-by-2 crib configuration is most common, although 3-by-3, 3-by-2, 3-by-3, and 4-by-4 configurations have been considered and have found limited application.

Underground mines use large numbers of wooden cribs to provide support over an area between two opposing surfaces rather than at a point as with a wooden post. These opposing surfaces are referred to differently in different mining industries. For example, the lower surfaces in mines may be referred to as the floor or footwall, and the upper surfaces as the roof or hanging wall. Typically, cribs are more extensively used in longwall and high extraction room-and-pillar coal mining. Cribs are also extensively used in non-coal underground mining.

A crib is typically constructed of wooden elements of square or prismatic cross-section, 5 to 6 inches across, although other shapes have also been used. The length of elements used typically varies from 30 inches to 60 inches, depending upon the height of the area to be supported. The term ‘aspect ratio’, when used in conjunction with a crib, denotes the ratio of the height of the crib to the distance between centers of contact areas along a timber. Reducing aspect ratio increases the stability of the crib structure, and ratios larger than 2.5 and less than 4.3 are recommended. A crib structure should be designed to have appropriate rigidity, or stiffness, and load carrying capacity to provide early, controlled resistance to rock mass movement to maintain excavation stability.

A typical crib uses solid, prismatic wooden crib elements of 5″-by-5″-by-30″ or 6″-by-6″-by-36″, although other sizes may be used. The load is transferred between upper and lower surfaces through typically four contact areas in a horizontal plane of the size 5″-by-5″ or 6″-by-6″ depending on the size of the crib element. Except at and around the contact areas, there is very little stress or force within the prismatic element. The areas adjacent to the contact areas are in tension while zones away from contact areas have almost no stresses vertically or horizontally. At and below the contact areas are high compressive stresses due to load transfer.

Wood is a transversely isotropic material with much higher strength and stiffness when loaded axially, or parallel to the grain, as compared to loading transversely, or perpendicular to the grain. More specifically, a typical oak timber loaded axially has a compressive strength of 2000-2500 psi and an elastic modulus of 150,000-250,000 psi. Similar data for the two lateral loading directions are about equal to each other, and a typical oak timber has a compressive strength of 500-700 psi and an elastic modulus of 25,000-35,000 psi. Furthermore, the Poisson's ratios for loading in the axial and lateral directions are also significantly different: 0.10-0.20 for loading axially and 0.30-0.40 for loading in the two lateral directions. The type of wood and the engineering data included here are provided as an example and these may vary over a wide range.

A typical solid wood cribbing for support has several disadvantages, including: low rigidity, a limited load carrying capacity, a high resistance to airflow, heavy weight per crib element, limited pre-load capacity, insufficient post-failure characteristics, flammability, and shrinkage.

A typical wood crib's rigidity is low since wood is loaded at right angles to grain. So; the support column allows a significant amount of deformation, as much as 20% of the total height of the column may be reduced through deformation.

Because of large deformations, the column has limited load carrying capacity; a typical crib column fails due to buckling before achieving its full load carrying capacity.

Air flow in mines is important. Since each crib column reduces the available air flow space when installed, resistance to air flow can be significant.

Installing typical solid wood crib element is difficult in locations where the surfaces are not parallel to each other or irregular.

Each wooden crib element typically weighs about 35 pounds, making carrying them by hand and assembling a crib column an arduous process, especially when one must lift an element above one's head.

Since low-rigidity wedges, cut parallel to the wood grain, are typically used to preload the crib, the amount of preload force that can be introduced to a column is limited and it tends to decay with time. The wedges typically deform under low loads, which means that the column does not support significant loads until the upper and lower surfaces have deformed toward each other, through compression of the column. Preloading is currently applied through wooden wedges, typically 3 to 4 inches wide that are cut at inclination angles of 10 to 20 degrees. These wedges are loaded transversally to the wood grain and yield at the low pressure of 500 to 700 psi. For wedges cut at high inclination angles, the contact areas with prismatic crib elements are small. Therefore, stress concentrations at contact points are high and the wedges yield even at low crib loads. The wedges then become loose providing little or no preload on the installed crib. Industry professionals suggest that there is a need to develop a relatively simple mechanism to apply a sustained preload of 5 to 8 tons when a crib is installed. Moreover, wood shrinks as it loses moisture. Upon shrinking it loses the preinstalled load and industry is seeking ways to minimize this problem.

In addition to the above, the post-failure characteristics of wood do not provide a relatively flat load-deformation curve and wood is flammable.

The use of steel or other similar material for mine support and tunnel cribbing would solve most of the problems inherent in the wood cribbing. Steel is more rigid than wood, and, when used in a support column, has a greater load carrying capacity without the risk of buckling failures present in wood cribbing. A steel crib support column can support a sustained preload when it is installed and does not lose this preinstalled load through shrinking, as is common in wood cribbing. Additionally, steel provides a relatively flat post-failure load-deformation curve and steel is not flammable. However, despite the advantages of using steel, it has only found limited use as a material in cribbing elements because solid steel is heavy and expensive. Understandably, steel would not be a suitable material to construct prior art cribbing elements; a conventional solid cribbing element made of steel would be very heavy. Steel has been extensively used in steel supports such as arches, and bars (U.S. Pat. Nos. 3,991,580; 3,952,525; 7,909,542; 5,484,130), and either as reinforcement for concrete (U.S. Pat. No. 4,497,597) or as only a part of the load carrying element in wood (WO 00/53892) and cement-concrete (U.S. Pat. No. 4,565,469) crib elements.

The present invention utilizes an innovative design to construct a light-weight steel crib element with all of the desired characteristics for a crib element as well as low resistance to airflow. Furthermore, the innovative design should find applications beyond mining and tunneling industries such as in construction, railroad and ship building industries.

SUMMARY OF THE INVENTION

This invention provides an improved cribbing support in mines and tunnels through a lightweight, engineered steel crib element to provide support between two surfaces. It is easy to carry manually and offers very low resistance to airflow depending upon the selected embodiment. The elements can be used in multiple ways to construct cribs. The element provides high stiffness support to develop a crib with literally any desired load carrying capacity. However, it is anticipated that initially cribbing with load carrying capacity of 100-tons to 300-tons will be commonly used to minimize rock mass movement in mines and tunnels.

The steel crib element consists of one or more center elongate structural elements, connected at the distal ends of the elongate structural element to at least two outer hollow or solid steel load carrying members. The hollow or solid steel load carrying members may be perforated with holes, and loaded axially or parallel to its longitudinal axis, or laterally or perpendicular to its longitudinal axis depending upon a selected embodiment among the many in each configuration. The hollow load carrying members may be internally reinforced or filled with appropriate materials to achieve desired load-deformation characteristics. The elongate structural elements may be prismatic or round or any other shape in cross-section and may use steel or any other suitable material (metal, non-metal, polymer composites, etc) that have appropriate load carrying capacity, load-deformation characteristics, and material cost. The connection between elongate structural elements at the distal ends and load carrying members may be through nuts and bolts, welds, screws, or other suitable fastening means or polymeric materials. The elongate structural elements, connecting the load carrying members, may also be interconnected among themselves at suitable intervals to provide required flexural rigidity and load carrying capacity in different spatial planes. The crib structure is constructed similar to wooden cribbing by superimposing only these crib support elements in 2×2 layers, 2×3 layers, 3×3 layers, or other suitable layered system. To ensure full contact area between load carrying members of different elements and to minimize likelihood of slippage or limit lateral movement between mating surfaces of different elements, the crib element design includes indexing as well as interlocking stops. The upper and lower plates installed on the hollow load carrying steel tubes may be flat with skid resistant material on the top, “diamond plate” design with curved raised surfaces to allow interlocking and minimize lateral movement or slippage, embossed with suitable design, or may have short pins that fit into holes in the mating plates depending upon the embodiment selected.

The novel crib element offers the following advantages: it has much higher stiffness (10-20 times or more) than the wooden cribs (about 40,000 psi) commonly used today; it can be designed to have variable stiffness; it can be designed to support any loads but typically varying from 100 tons to 300 tons for a 6-ft high cribs; it has the ability to sustain almost peak load even after the steel starts to yield; it is lightweight; it may offer very low resistance to airflow in underground mine roadways; and, it does not shrink like the wooden cribs that are almost exclusively used today in mining and tunneling industries.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1—(a) A side view of a steel crib element with a solid load carrying member and a flat plate or bar elongate structural element; (b) A top view of the steel crib element.

FIG. 1A—(a) A sectional view of a steel crib element with hollow load carrying members and a flat plate or bar elongate structural element; (b) Another sectional view of the steel crib element.

FIG. 1B—(a) A top view of a steel crib element with hollow load carrying members with recessed grooves for mating adjoining steel crib elements and a flat plate or bar elongate structural element; (b) A sectional view of the steel crib element.

FIG. 1C—(a) A top view of a steel crib element with hollow octagonal load carrying members and a flat plate or bar elongate structural element; (b) A sectional view of the steel crib element. This figure may need revision.

FIG. 1D—(a) A side view of a steel crib element with hollow perforated load carrying members and a flat plate or bar elongate structural element; (b) A top view of the steel crib element.

FIG. 1E—(a) A sectional view of a steel crib element with hollow load carrying members with indexing and mating top and bottom caps and a flat plate or bar elongate structural element; (b) A top view of the steel crib element.

FIG. 1F—(a) A top view of a steel crib element with hollow cylindrical load carrying members and two interconnected elongate structural elements; (b) A sectional view of the steel crib element.

FIG. 1G—(a) A top view of a steel crib element with three hollow load carrying members and interconnected elongate structural elements; (b) A side view of the steel crib element.

FIG. 1H—(a) A top view of a steel crib element with hollow load carrying members and two interconnected elongate structural elements; (b) A side view of the steel crib element.

FIG. 2—(a) A sectional view of a steel crib element with hollow load carrying members reinforced internally with steel plate and two interconnected elongate structural elements; (b) Another sectional view of the steel crib element.

FIG. 3—(a) A top view of a steel crib element with hollow load carrying members with cylindrical mating and indexing elements and two interconnected elongate structural elements; (b) A sectional view of the steel crib element.

FIG. 4—(a) A top view of a steel crib element with hollow load carrying members with diamond pattern cap plates and two interconnected elongate structural elements; (b) A side view of the steel crib element.

FIG. 5—(a) A sectional view of a steel crib element with hollow steel load carrying members with wood reinforcements and two interconnected structural elements; (b) Another sectional view of the steel crib element.

FIG. 6—A perspective view of the crib elements stacked into a 2×2 crib structure.

FIG. 7—A planar view of stacked crib elements forming a crib support between the mine floor and roof.

FIG. 8—A planar view of stacked crib elements forming a crib support between the mine hanging wall and footwall.

Reference Numerals in Drawings Reference Numerals in Drawings  1 Steel Crib Element  5 Mine Floor  6 Mine Roof  7 Hanging Wall  8 Footwall  9 Wedges 10 Elongate Structural Element 21 Hollow Load Carrying Member 22 Solid Steel Load Carrying Member 27 Round or Prismatic Bar Elongate Structural Elements 28 Triple Reinforcing Bar Elongate Structural Elements 36 Interconnections Between Elongate Structural Elements 25 Raised Lateral Movement-Resistant Material (Diamond Plate) 23 Cylindrical Indexing and Mating Element 26 Flat Bar Elongate Structural Elements 31 Fastening Means 32 Flat Bar Internal Reinforcements 40 Sides of Load Carrying Member 42 Load Carrying Outer Surface 44 Indexing Protrusion 46 Indexing Grooves 47 Octagonal Top of Load Carrying Member 48 Sides of Octagonal Load Carrying Member 52 Perforated Structural Element 54 Top or Bottom Cap with Mating Protrusions 55 Bottom or Top Cap with Mating Grooves 56 Cylindrical Load Carrying Member 62 Hollow 64 Wood or Other Material Reinforcements

DETAILED DESCRIPTION

A conceived steel crib may consist of two or more pieces of metal load carrying members of any geometrical cross-section connected to each other through one or more elongate structural elements. The elongate structural elements may be rod of any shape or plate metal or any other material that provides appropriate load-deformation characteristics prior to and after yielding, has appropriate flexural rigidity in different orientations, and is reasonable in cost. The material used may also have any geometry that satisfies the above requirements. Mechanistically, the size of the load carrying member, its wall thickness, its geometry (square, rectangle, circular), and its loading orientation control its stiffness and load-deformation characteristics. The elongate structural elements may be metal rod or bar, non-metal, or polymers. The elongate structural elements may be interconnected at suitable intervals to provide appropriate strength and stiffness in different spatial planes. Similarly, the internal hollow portion of the hollow load carrying members may be reinforced with any material such as: metal, wood, plastic, and cementitous or pozzolonic material in various geometric configurations to achieve desired strength and to further modify the load-deformation characteristics of the crib element. The type and spatial distribution of lateral connections between the tubes (round, prismatic, solid, hollow) and the type of reinforcements (square, round, prismatic) between the lateral connections allow the ability of the crib to carry differential loading in different planes and twisting of the cribbing structure. The crib element is loaded so that it is either loaded transversely or loaded axially with respect the axis of the load carrying members.

In the embodiments where the hollow tube load carrying member is loaded axially, the upper and/or lower surfaces of the load carrying member may be covered with a lateral-movement resistant designs including but not limited to the following: solid or perforated steel plate; steel plate with roughened surfaces, such as “diamond plate” material available commercially; suitably embossed plates of any material, any thickness, and any shape; or protruded surfaces on one end with appropriate mating surfaces on the other end.

Additionally, the design of the hollow load carrying member may be shaped to provide interlocking between stacked crib elements.

To date, all experimental studies have been performed on Grade B or Grade C steel 30-inch long crib elements with load carrying members constructed of ASTM A-500 steel tube of 3/16-inch wall thickness. Grade B steel has a minimum yield stress of 46,000 psi and minimum tensile strength of 58,000 psi, while Grade C has a minimum yield stress of 50,000 psi and minimum tensile strength of 62,000 psi. The elongate structural elements also have similar strength and elastic properties. Steel tubes with up to 100,000 psi yield stress are available in a variety of wall thicknesses. Several of these may provide feasible desired crib element but the weight of the element and cost of the element could be very different.

The design of the structure above allows it to be lightweight, with the ability to withstand large amount of deformations because of the characteristics of steel or other materials used and reinforcements within the hollow load carrying members. The weight of each crib element will vary based on load carrying capacity. For a single element with ability to carry about 120-tons of load for a 2×2 crib, the weight of the designed element is only 20-21 pounds. Since most cribs used in mining and tunneling applications are designed to carry loads varying from 100-tons to 200-tons with four loading surfaces, all embodiments tested are suitable for use in mine and tunnels. The design of the cribs may be varied to meet the load carrying requirements of different structural applications.

The length of the load carrying members and elongate structural elements can be varied to achieve desired aspect ratio (height to width ratio). All studies to date have been performed on 30-inch or 36-inch long steel cribs with two load carrying steel members per crib. Longer cribs such as 42-inch, 48-inch, 54-inch, or 72-inch cribs can easily be developed based on this disclosure by adjusting the dimensions of the load carrying members and elongate structural elements and/or by connecting three or four load carrying members in series. Crib elements with three or four load carrying members may be configured at equi-distances along the length of the crib element (a preferred embodiment) or staggered.

The overall cribbing structure is constructed similarly to conventional wooden cribbing structure and that is by stacking crib elements. The cribbing structure is tightened between the roof and floor or hanging wall and footwall through steel inserts, wedges, grout bags, wooden wedges or other suitable materials which have high rigidity and will not shrink. Thus, a high preload can be applied to the crib during its construction process. Preferably, the material used for the wedges has a similar stiffness to the load carrying member to apply a maximum preload to the constructed steel crib structure. In preferred embodiments, the wedges are constructed of steel and are 3-inches wide to 5-inches wide to keep their weight to a minimum. Other sizes and materials for tightening the crib are within the scope of this invention. The steel wedges or inserts can also be manufactured from hollow steel tube.

The embodiments of the present invention are best described in reference to the figures. The crib element embodied in FIG. 1 is constructed of two 6-inch×6-inch×6-inch pieces of solid steel as the load carrying structural members 22; these load carrying structural members 22 are connected through an elongate structural element 10 composed of A36 steel flat bar 26, 6-inch wide and ⅛-inch thickness. Other gauges of steel or other materials may be used. This elongate structural element 10 is attached at the distal ends to the load carrying member 22 via fastening means 31 such as welds or bolts. Alternately, other metals with other dimensions may be used as the load carrying member 22 for specific applications. Furthermore, the load carrying member 22 does not have to be square in cross-section. The elongate structural element 10 in this embodiment may also be composed of flat bar or plate sizes varying from 3-inch to 10-inch wide or more, with thicknesses ranging from ⅛-inch to ½-inch. The crib element is loaded perpendicular to the axis of the load-carrying structural member 22. The load carrying capacity of this embodiment is about 80-tons.

The crib element embodied in FIG. 1A is constructed of two 6-inch×6-inch steel tubes with 3/16-inch wall thickness as the load-carrying structural members 21; these hollow load-carrying structural members 21 are connected through an elongate structural element 10 composed of A36 steel flat bar 26, 6-inch wide and ⅛-inch thickness attached to the load carrying member 21 at the distal ends via fastening means 31 such as welds or bolts. Alternatively, other gauges of steel may be used and other metals may be used for both the elongate structural element 10 and the load carrying member; and other tubing sizes (3-inch to 10-inch or more), with different wall thicknesses (0.125 inch to 0.5-inch) could be used as the load carrying member 21. Furthermore, the tubes do not have to be square in cross-section. The elongate structural element 10 in this embodiment may also be composed of flat bar or plate sizes varying from 3-inch to 10-inch wide, with thicknesses ranging from ⅛-inch to ½-inch or more. The crib element is loaded perpendicular to the axis of the hollow load carrying structural member 21. The load carrying capacity of this embodiment is about 80-tons.

Alternately, to ensure full contact area between load carrying members of different elements and to minimize lateral movement between mating surfaces of different elements, the crib element design may include different designs for indexing or mating elements as well as limiting displacements under load between the mating elements. The upper and lower plates installed on the hollow load carrying steel tubes may also be embossed, may have short pins that fit into holes in the mating plates, or have curved raised surfaces to provide interlocking and indexing. In the embodiment represented in FIG. 1B, the load carrying member has the addition of indexing grooves 46 and protrusions 44 to enable mating between crib elements to impart structural stability in the constructed cribbing structure. The load bearing element 21 in this embodiment can be open at the top and/or bottom.

Indeed, mating of upper and lower surfaces of elements in a crib structure can be accomplished through a variety of methods, such as in the embodiment represented in FIG. 1E, with the addition of top and/or bottom caps with mating protrusions 55 and grooves 56. The mating protrusions and grooves can be of any shape and size as long as they are complementary. Indeed, complementary mating protrusions and grooves can also be embossed into the metal load-carrying member or can be accomplished through complementary perforations 52 in the load carrying member as represented in FIG. 1D. The implementation of perforations 52 in the load-carrying structural member 21 also imparts another advantage in that the weight of the overall crib element is reduced for applications where crib weight is critical.

In the embodiment represented in FIG. 1C, the load carrying member 47 is octagonal in cross section. In this embodiment, the octagonal load carrying member 47 is hollow and has sides 48. The embodiment represented in FIG. 1F has a hollow cylindrical load carrying structural member 56. Indeed, the load carrying members can be some shape other than circular, octagonal, or square in cross-section. The load carrying member can be any shape in cross-section, including hexagonal, triangular, or polygonal.

In another embodiment of the present invention, represented in FIG. 1G, three load carrying members 21 are connected in series. These load carrying members 21 are connected through elongate structural elements 10 comprising two round bar elongate structural elements 27 with flat bar interconnections 36 between them in a truss configuration; this configuration better disseminates normal and shear stresses within the structure but other configurations and materials can be used depending on the application. More than three load carrying structural members can be connected in series at equi-distances or in staggered configurations for desired applications.

The crib element embodied in FIG. 1H is constructed of two 6-inch×6-inch steel tubes with 3/16-inch wall thickness as the load-carrying structural members 21; these hollow load-carrying structural members 21 are connected through an elongate structural element 10 composed comprising two round bar elongate structural elements 27 of ⅝-inch diameter A36 steel round bar with three steel flat bar interconnections 36 between them. Alternatively, other gauges and sizes of steel may be used and other metals may be used for the elongate structural element 10, the interconnections 36, and the load carrying members 21; and other tubing sizes (3-inch to 10-inch or more), with different wall thicknesses (0.125 inch to 0.5-inch) could be used as the load carrying member 21. In this embodiment the opposing sidewalls are missing creating an open-ended cavity 62.

In another embodiment of the present invention, represented in FIG. 2, the load carrying member 21 is constructed with 6-inch×6-inch steel tube with 3/16-inch wall thickness with reinforcements 32 within each tube comprising two ⅛-inch×6-inch A36 steel plates in an X-configuration. Alternatively, the reinforcements 32 within the load carrying member 21 can be steel or metal of any configuration and gauge such as cylinders, bars, and triangles. These load carrying members 21 are connected through an elongate structural element 10 comprising two round bar elongate structural elements 27 of ⅝-inch diameter A36 steel round bar with three ¼-inch×¾-inch steel flat bar interconnections 36 between them. Alternatively, other gauges and sizes of steel may be used and other metals may be used for the elongate structural element 10, the interconnections 36, and the load carrying members 21; and other tubing sizes (3-inch to 10-inch or more), with different wall thicknesses (0.125 inch to 0.5-inch) could be used as the load carrying member 21. The load carrying capacity for this embodiment is about 140-tons.

Yet another embodiment of the present invention, constructed similarly to the crib element of FIG. 2, the load carrying member 21 is constructed with 6-inch×6-inch steel tube with 3/16-inch wall thickness with reinforcements 22 within each hollow tube load carrying member 21 comprising two 1-inch×6-inch A36 steel plates (one vertical and one horizontal.) These load carrying members 21 are connected through an elongate structural element 10 comprising two round bar elongate structural elements 27 of ⅝-inch diameter A36 steel round bars with one steel flat bar interconnection 36 between them. Alternatively, other gauges and sizes of steel may be used and other metals may be used for the elongate structural element 10, the interconnections 36, the reinforcements 22, and the load carrying members 21; and other tubing sizes (3-inch to 10-inch or more), with different wall thicknesses (0.125 inch to 0.5-inch) could be used as the load carrying members 21. The load carrying capacity for this embodiment is about 120-tons.

In yet another embodiment of the present invention, constructed similarly to the crib element of FIG. 2, the load carrying member 21 is constructed with 6-inch×6-inch steel tube with 3/16-inch wall thickness with cylindrical reinforcements within each tube comprising 1/16-inch thick steel tube. The cylindrical reinforcements 23 within each load carrying member 21 can be of similar height to the structural member or slightly smaller to be contained completely within the load carrying member 21. These load carrying members 21 are connected through an elongate structural element 10 comprising two round bar elongate structural elements 27 with three ¾-inch×¾-inch steel flat bar interconnections 36 between them. Alternatively, other gauges and sizes of steel may be used and other metals may be used for the elongate structural element 10, the interconnections 36, the reinforcements 22, and the load carrying members 21; and other tubing sizes (3-inch to 10-inch or more), with different wall thicknesses (0.125 inch to 0.5-inch) could be used as the load carrying members 21.

In a similar embodiment, the load carrying member 21 is constructed with 6-inch×6-inch steel tube with 3/16-inch wall thickness with a cylindrical reinforcements within each tube. These load carrying members 21 are connected through an elongate structural element 10 comprising two round bar elongate structural elements 27 with interconnections 36 between them. This crib element is loaded axially and the load carrying members 21 are constructed so that the hollow tube load carrying member 21 of one element rests at right angles to the hollow tube load carrying member 21 of the upper or lower element. In this configuration, each steel tube load carrying member 21 is allowed to yield and punch into the lower or upper tube. The two punched tubes interlock and provide load carrying and buckling strength to the crib. This embodiment of the present invention with a 6-inch square hollow steel tube load carrying member 21 and a 6-inch high cylindrical reinforcement 23 carried about 160-tons. Alternatively, other gauges and sizes of steel may be used and other metals may be used for the elongate structural element 10, the interconnections 36, the reinforcements 22, and the load carrying members 21; and other tubing sizes (3-inch to 10-inch or more), with different wall thicknesses (0.125 inch to 0.5-inch) could be used as the load carrying members 21. This design can be modified for different load carrying capacity and stiffness.

In another embodiment of the present invention, represented in FIG. 3, the load carrying member 21 has a cylindrical mating and indexing element 23 running substantially through the load carrying member 21. In this embodiment, the cylindrical mating and indexing elements 23 are of similar height to the load carrying member 21 and slightly protrude through the top (providing a recess in the bottom of the element) to provide indexing and mating of upper and lower crib elements. This configuration also provides reinforcement to the load carrying member 21. Alternatively, cylindrical mating and indexing element 23 may be composed of two separate elements: one a protrusion extending from the top of the load carrying member and the other a recess in the bottom of the load carrying member. Additionally, the cylindrical mating and indexing elements 23 need not be cylindrical and can be almost any shape in cross section including square or octagonal.

Yet another embodiment of the present invention, represented in FIG. 4, the load carrying member 21 is constructed with 6-inch×6-inch hollow steel tube with 3/16-inch wall. These load carrying members 21 are connected through an elongate structural element 10 comprising two round bar elongate structural elements 27 with three ¼-inch×¾-inch steel flat bar interconnections 36 between them. This crib element is loaded perpendicular to the axis of the load carrying member 21 and has ¼-inch×6-inch×6-inch raised-floor steel plates 25 attached to the top and bottom of the load carrying members 21 via fastening means. The use of the diamond-pattern raised floor steel plates 25 allowed only about 0.25-inch of lateral displacement between the two mating steel cribs while carrying over 200-tons (limited by the capacity of the testing machine.) Again, alternatively, other gauges, configurations, and sizes of steel may be used and other metals may be used for the elongate structural element 10, the diamond-pattern raised floor plates 25, the interconnections 36, and the load carrying members 21; and other tubing sizes (3-inch to 10-inch or more), with different wall thicknesses (0.125 inch to 0.5-inch) could be used as the load carrying members 21.

In another embodiment of the present invention, represented in FIG. 5, the hollow load carrying member 21 is reinforced with a prismatic wooden element 64. These load carrying members 21 are connected through an elongate structural element 10 comprising two round bar elongate structural elements 27 of ⅝-inch diameter A36 steel round bar with three ¼-inch×¾-inch steel flat bar interconnections 36 between them. The crib element was loaded axially. This significantly increased the load carrying capacity and improved the post-failure load-deformation properties. The above characteristics can also be achieved by reinforcement of the hollow load carrying member 21 with a cementitious or pozzolonic material, polymeric material, metallic or non-metallic material, or any other suitable material. With such reinforcements, the load carrying member may be loaded axially or transversely. Alternatively, other gauges and sizes of steel may be used and other metals may be used for the elongate structural element 10, the interconnections 36, and the load carrying members 21; and other tubing sizes (3-inch to 10-inch or more), with different wall thicknesses (0.125 inch to 0.5-inch) could be used as the load carrying members 21.

Yet another embodiment of the present invention, where the crib elements 1 are stacked in a 2×2 crib structure, is represented in FIG. 6. The crib structure is constructed of crib elements comprising two 6-inch×6-inch steel tubes with 3/16-inch wall thickness as the load carrying members 21; these hollow load carrying members 21 are connected through an elongate structural element 10 comprising three (3), ½-inch diameter steel concrete reinforcing rods 28, without any interconnection between the rods. The elongate structural element runs along the entire length of the crib element 1, and is attached to the far interior of the hollow load carrying member 21 via fastening means 31 such as welds or bolts; this configuration allows the elongate structural element 10 to also provide reinforcement to the load carrying member. These crib elements 1 are loaded transversely.

Yet another embodiment of the present invention, where the crib elements 1 are stacked in a 2×2 crib structure between the floor 5 and roof 6 of a mining excavation, is represented in FIG. 7. The first and second lower crib elements 1 are spaced apart substantially parallel to each other and placed on the floor 5. The upper first and second crib elements 1 are then placed on top of the lower first and second crib elements 1. These first and second upper crib elements 1 are aligned parallel to each other and placed orthogonally with respect to the orientation of the lower first and second crib elements 1. These crib elements 1 are stacked in such a manner between the roof 6 and floor 5 of a mine and a preload is applied through the use of suitable material wedges 9.

Another embodiment of the present invention, where the crib elements 1 are stacked in a 2×2 crib structure between the hanging wall 7 and footwall 8 of a mining excavation, is represented in FIG. 8. The first and second lower crib elements 1 are spaced apart substantially parallel to each other and placed on the footwall 8. The upper first and second crib elements 1 are then placed on top of the lower first and second crib elements 1. These first and second upper crib elements 1 are aligned parallel to each other and placed orthogonally with respect to the orientation of the lower first and second crib elements 1. These crib elements 1 are stacked in such a manner between the hanging wall 7 and footwall 8 of a mine and a preload is applied through the use of suitable material wedges 9.

Although the above discussion relates to steel construction, the principles apply equally to construction of similar designs using other materials. The sizes of the load carrying members, elongate structural elements, and reinforcements indicated throughout the application are only suggestions and not meant to be limiting. The developed concepts can also be utilized in the design of tunnel arches. 

1. An engineered metal crib element comprising: an elongate structural element having first and second opposing distal ends having attached thereto respectively first and second load carrying members; and where each load carrying member has upper and lower caps proximately vertically spaced apart and said upper and lower caps having respective substantially flat upper and lower contact surfaces that are substantially parallel one with respect to the other and where said upper and lower caps are connected there between and supported by a load carrying member.
 2. The engineered metal crib element of claim 1, wherein the first and second load carrying members are stainless steel.
 3. The engineered metal crib element of claim 2, wherein the load carrying members have an internal hollow space substantially surrounded by a stainless steel wall.
 4. The engineered metal crib element of claim 3, further comprising a reinforcement member within the internal hollow space of the first and second load carrying members and said reinforcement member extending between and contacting at least two opposing walls.
 5. The engineered metal crib element of claim 3, wherein the reinforcement within the load carrying member substantially fills the hollow space of the load carrying member.
 6. The engineered metal crib element of claim 5, wherein the reinforcement within the load carrying member is a plurality of plates horizontally extending from a common center vertical axis.
 7. The engineered metal crib element of claim 3, wherein the reinforcement within the load carrying member is a solid wood member.
 8. The engineered metal crib element of claim 1, wherein surfaces of the upper and lower caps are not smooth to thereby resist lateral movement.
 9. The engineered metal crib element of claim 8, wherein the surfaces are etched to thereby create an uneven surface.
 10. The engineered metal crib element of claim 1, further comprising protrusions in the upper cap and grooves in the lower cap of each load bearing structural member, where the protrusions and the grooves are complimentary one with respect to the other for resisting lateral movement.
 11. The engineered metal crib element of claim 10, wherein the complementary protrusions and grooves are complimentary raised and recessed perforations respectively.
 12. The engineered metal crib element of claim 1, further comprising at least two elongate structural elements.
 13. The engineered metal crib element of claim 12, further comprising at least one member extending between and interconnecting the elongate structural elements.
 14. The engineered metal crib element of claim 1 further comprising at least one additional load carrying members where the at least one additional load carrying member is disposed and aligned between first and second load carrying members and attached along the elongate structural element.
 15. An engineered metal crib support structure comprising: spaced apart upper first and second crib elements and spaced apart lower first and second crib elements; where said upper first crib element has a first elongate structure having first and second opposing distal ends having attached thereto respectively first and second load carrying members and where said upper second crib element has a second elongate structure having third and fourth opposing distal ends having attached thereto respectively third and fourth load carrying members; where said lower first crib element has a third elongate structure having fifth and sixth opposing distal ends having attached thereto respectively fifth and sixth load carrying members and where said lower second crib element has a fourth elongate structure having seventh and eighth distal ends having attached thereto respectively seventh and eighth load carrying members; where each load carrying members have upper and lower caps proximately vertically spaced apart and said upper and lower caps having respective substantially flat upper and lower contact surfaces that are substantially parallel one with respect to the other and where said upper and lower caps are connected there between and supported by a load carrying member; and where said spaced apart upper crib elements extend substantially parallel one with respect to the other and where said first and third load carrying members of said upper crib elements are vertically aligned immediately above fifth and seventh load carrying members of a lower crib elements and where said second and fourth load bearing members of said upper crib elements are vertically aligned immediately above sixth and eighth load carrying members and where said spaced apart lower crib elements extend substantially parallel one with respect to the other.
 16. An engineered metal crib support structure comprising: a spaced apart upper first and second crib element pair and a spaced apart lower first and second crib element pair, where each crib element in the upper and lower crib element pairs has an elongate structure having distal opposing ends where each of said opposing ends has a load carrying member attached thereto and where each load carrying member has upper and lower caps proximately vertically spaced apart and said upper and lower caps having respective substantially flat upper and lower contact surfaces that are substantially parallel one with respect to the other and where said upper and lower caps are connected there between and supported by a load carrying member; where said spaced apart upper first and second crib element pair is oriented to extend substantially parallel one with respect to the other and said spaced apart lower first and second crib element pair is oriented to extend substantially parallel one crib element with respect to the other and extend substantially orthogonal with respect to the orientation of the, upper first and second crib element pair; and where each of said load carrying members of the spaced apart upper first and second crib element pair are aligned vertically above one of said load carrying members of the spaced apart lower first and second crib element pair and thereby structurally supported. 